Green, G9 and slowblow mic pre.

[FotisGR]

if you use 4x 7812 you should lift the (single) voltage going into the four Vregs, not lift each seperate output.

:thumb: This is what i was looking for... :grin:

Thank you very much
fotis

 

[sismofyt]

since you got four chokes, you can make a better PSU. what kinda caps are you gonna hook up to those suckers?

 

[FotisGR]

In my bench there are 6 pieces of big blue Sprague 470uf/385V , 20 pieces Nichicon 100uf/400V (105C low ESR) and a Toroid transformer 250V/300mA.

 

[sismofyt]

what are you planning to use?

 

[FotisGR]

I never had a pre like this. More enjoyable is that is point to point construction so i can test everything. Caps, txs, everything. By the way today i tested a tl783 reg. I powered it via tl783 320V and vs RCRC psu. I can say that there is difference. Not big but no small, too. I never had a test like this. I also found that going HV to 350-360 is sound more nice for me. More clear mid and something like more linear...


More funny story of the day is that i drive the 5687 from the 1176 compressor's signal pre out. I took the signal from R27 1176's pot and i directly going to 1k 5687 input's resistor. It's fantastic :shock: . It took all the 1176's aggresive sound and make it gentleman. I can't explain it with words. If you want to know what i mean give it a try.

So if you want DIY just try it :thumb:

Cheers
Fotis

 

[sismofyt]

yes, raising the B+ to a near 400V is great for SRPPs

and yup, the 5687 SRPP is an exellent linedriver. you can get even better sound if you eliminate the grid resistors, but check for oscillation

 

[FotisGR]

what are you planning to use?

I don't know yet. I am going to check what is like to my ears. I am more pleasant with dynamics and super linearity. I hate some slow rate like snakes tube sounds or muddy, fat sounds etc.For start i think a CRCLC (point for 5687) to continue LC (point to 12au7) for each channel, but i am not sure. Do you have a better idea ? I would try a tube rectifier but i haven't such trafo for this. Maybe another time.

Cheers
fotis

 

[sismofyt]

well, i designed the pre to meet those criterias exactly, not to sound toobey or vintage (tm Neve), so you should stick to the basic design. a tube rectifier will not do good here, it's important to keep the PSU low impedance. but improvements can be made in the PSU with the components you got. do you want me to draw up something?

one day if you have time, you could try and use another tube than the 12AU7, the 6SN7 (use 12SN7 - same tube, but with 12,6V heater)

nice lab you got

 

[Emperor-TK]

So do I understand this right.... The purpose of biasing the heaters is because the cathodes are at a high potential because of the 1K cathode resistors? What happens when the heaters are at 12V and the cathode is at say, +100V? Does the heater begin to emit electrons and act as a cathode itself?

This might be a bit advanced for me, but I'll ask anyway. Why are the cathodes floated so high to begin with?

Thanks,
Chris

 

[rafafredd]

It shorts. Have a look at the datasheet of some tubes. It genarally has a maximum heater-cathode voltage.

LA2A has a white cathode follower at the output but it seems that no one lifts the heaters. And I don´t think there is many LA2A shorted output tubes out there...

But anyway, some says lifting (or biasing) can also make the amplifier quieter.

 

[sismofyt]

yes, it can help with the hum level. most tubes can survive a too big potential, but SRPPs must be biased up

 

[FotisGR]

but improvements can be made in the PSU with the components you got. do you want me to draw up something?

I found 2 big Solen MKP 22uf/400V , too. :wink:
Ofcource i want. :thumb:
And many diyers would want, too

Cheers
fotis

 

[FotisGR]

one day if you have time, you could try and use another tube than the 12AU7, the 6SN7

I will try to find this tube from a friend . I have tons of thinks on my bench but no tubes . But i have a friend with a great tube collection. He gave me for Slowblow 5 JAN-5687WB by General Electric and 2 ecc82 by Mullard :grin:

(use 12SN7 - same tube, but with 12,6V heater)

I am not sure that i understand. My Slowblow's prototype heatres powered by a LM338 adj for 12.6VDC.

 

[FotisGR]

Having 4 10H/200mA toroid chokes, what is the best way to use them on 2ch slowblow mic pre?
The last 2 weeks i was very very busy , so i haven't finished the project yet :sad:

Cheers
fotis

 

[FotisGR]

I finally finished. Thank you all for your help and especially Sismofyt and Jazzy Pidjay.

How it sounds? Really you can't imagine..

http://www.qsl.net/sv3eao/123_2382.jpg
http://www.qsl.net/sv3eao/123_2383.jpg
http://www.qsl.net/sv3eao/123_2389.jpg
Cheers
fotis

 

[Viitalahde]

Nice work! :thumb:

 

[tony dB]

I must have missed something in this thread ....
do you build this in 30 minutes? Is this your version of the SloBlo?

(worked to much hours last week, my head hurts, and I want to finish some G9's soon, so sorry for my SloMentalState)

Tony

 

[tony dB]

Looking at my avatar, i just found out about my headaches...

 

[toffifee]

Hello Fotis! Looks really great! :thumb:
I´m just starting to build a slowblo, have collected all the parts, am doing metalwork at the moment (mounting the tube sockets).
Could you give me/us some more infos?
Most important question for me: How did you do the heater biasing? To which voltage do you bias the heaters? Which values at the resistors/the cap? Do you use the biasing as a bleeder for the HV, or do you use an additional bleeder?
Ole mentions on his site that you have a different design around the first tube?
And is your power supply the same as shown in the old versions of the circuit-diagram?
You see: I´m very curious :wink:
Thanks a lot; Toff

 

[FotisGR]

do you build this in 30 minutes? Is this your version of the SloBlo?

No this isn't the prototype 30' version but is still based on slowblow version :grin:

How did you do the heater biasing? To which voltage do you bias the heaters? Which values at the resistors/the cap? Do you use the biasing as a bleeder for the HV, or do you use an additional bleeder?

I biased at 60V above. I don't use extra bleeders. I just use only this resistors for bleeder.
I did for you a small shematic. I think it will help http://www.qsl.net/sv3eao/heaterbias.bmp

Ole mentions on his site that you have a different design around the first tube?

Yes. The last two months i test some configurations-topologies on my project. This project is a 2 channel mic pre so, the one channel is the classic slowblow design with ecc82 by mullard on srpp and the 5687 by Raytheon on srpp, too. The components for both channels are the same quality so any audio differencies are because the tube configutation or tube quality by itself...
Having the one channel as reference i tried for the other channel (only for the first tube): 5687 srpp, 5687 plate follower and 12sn7 plate follower. too.
By the way i think that i am loved with the classic slowblow version. With Jensen Paper in oil caps and good psu this is really an orgasm mashine...
If i could describe the configurations i would say:
Classic = like a dynamite. Deep bass(and i mean very deep) extremelly clear , full of harmonics and dynamics.
5687 plate follower = A litle bit narrow sound. I think is sounds at the G9 way but is more clear and harmonically.
12sn7 plate follower (jazzy pidjay version) = Really magic sound. Smooth sound with special linearity. Big full sound . The next time i will try this tube on srpp configuration. Something on my mind say me that this will be a big gift for my ears....

Cheers
fotis